Anterograde
amnesia is a selective memory deficit, resulting from brain
injury, in which the individual is severely impaired in learning
new information. Memories for events that occurred before
the injury may be largely spared, but events that occurred
since the injury may be lost. In practice, this means that
an individual with amnesia
may have good memory for childhood and for the years before
the injury, but may remember little or nothing from the years
since. Short-term memory
is generally spared, which means that the individual may be
able to carry on a conversation; but as soon as he is distracted,
the memory of the conversation fades.

It is now becoming apparent that while anterograde
amnesia devastates memory for facts or events, it may spare
memory for skills or habits. Thus, an individual with amnesia
can be taught a new skill, such as how to play a game or how
to write backwards. The next day, the amnesic individual will
claim to have no memory of the prior session, but when asked
to try executing the skill, can often perform quite well -
indicating that some memories have been formed. It is an important
area of current research to document exactly which kinds of
memory can be formed in amnesia, and how this may be used
to help rehabilitate amnesic individuals.

Anterograde amnesia can occur following
damage to at least three distinct brain areas. The first,
and most well-studied, is the hippocampus
and associated areas in the medial
temporal lobes of the brain. The hippocampus
seems to act as a "gateway" through which new fact information
must pass before being permanently stored in memory. If it
is damaged, no new information can enter memory - although
older information which has already passed through the gateway
may be safe. Damage to the hippocampus (and medial temporal
lobes) can occur following stroke
or aneurysm to
one of the arteries which supplies blood to these areas, as
well as following epilepsy,
encephalitis,
hypoxia,
carbon monoxide poisoning, near-drowning or near-suffocation,
and the earliest stages of Alzheimer's
disease. Some damage to the hippocampus also occurs in
the course of normal aging.

Finally, anterograde amnesia can sometimes
occur following damage to the diencephalon - a set of structures
deep in the brain including the medial thalamic nuclei. Currently,
there is no good understanding of why damage to these brain
areas should sometimes result in a selective memory deficit
such as amnesia. Korsakoff's
disease is a syndrome which can damage the diencephalon
and cause anterograde amnesia.